Re: [PATCH v3 1/2] eal: add thread yield functions

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Oct 25, 2023 at 06:31:10PM +0200, Thomas Monjalon wrote:
> When running real-time threads, we may need to force scheduling
> kernel threads or other real-time threads.
> New functions are added to address these cases.
> 
> The yield functions should not have any interest for normal threads.
> Note: other purposes may be addressed with rte_pause() or rte_delay_*().
> 
> Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
> ---
>  lib/eal/include/rte_thread.h | 22 ++++++++++++++++++++++
>  lib/eal/unix/rte_thread.c    | 16 ++++++++++++++++
>  lib/eal/version.map          |  4 ++++
>  lib/eal/windows/rte_thread.c | 15 +++++++++++++++
>  4 files changed, 57 insertions(+)
> 
> diff --git a/lib/eal/include/rte_thread.h b/lib/eal/include/rte_thread.h
> index 8da9d4d3fb..139cafac96 100644
> --- a/lib/eal/include/rte_thread.h
> +++ b/lib/eal/include/rte_thread.h
> @@ -183,6 +183,28 @@ int rte_thread_join(rte_thread_t thread_id, uint32_t *value_ptr);
>   */
>  int rte_thread_detach(rte_thread_t thread_id);
>  
> +/**
> + * Allow another thread to run on the same CPU core.
> + *
> + * Lower priority threads may not be scheduled.
> + *
> + * Especially useful in real-time thread priority
> + * to schedule other real-time threads.
> + * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
> + */
> +__rte_experimental
> +void rte_thread_yield(void);
> +
> +/**
> + * Unblock a CPU core running busy in a real-time thread.
> + *
> + * Especially useful in real-time thread priority
> + * to avoid a busy loop blocking vital threads on a core.
> + * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
> + */
> +__rte_experimental
> +void rte_thread_yield_realtime(void);
> +
>  /**
>   * Get the id of the calling thread.
>   *
> diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
> index 36a21ab2f9..92b4e53adb 100644
> --- a/lib/eal/unix/rte_thread.c
> +++ b/lib/eal/unix/rte_thread.c
> @@ -5,9 +5,11 @@
>  
>  #include <errno.h>
>  #include <pthread.h>
> +#include <sched.h>
>  #include <stdbool.h>
>  #include <stdlib.h>
>  #include <string.h>
> +#include <time.h>
>  
>  #include <rte_errno.h>
>  #include <rte_log.h>
> @@ -227,6 +229,20 @@ rte_thread_detach(rte_thread_t thread_id)
>  	return pthread_detach((pthread_t)thread_id.opaque_id);
>  }
>  
> +void
> +rte_thread_yield(void)
> +{
> +	sched_yield();
> +}
> +
> +void
> +rte_thread_yield_realtime(void)
> +{
> +	/* A simple yield may not be enough to schedule kernel threads. */
> +	struct timespec wait = {.tv_nsec = 1};
> +	nanosleep(&wait, NULL);
> +}
> +
While I realise we discussed this earlier, and I also was the original
suggester of using sched_yield, I think just having just one function using
sleep is probably best after all.

/Bruce